Tunable magnetron



Patented Sept. 24,1946

TUNABLE MAGNETRON Percy Spencer, West Newton, Mass, assignor to RaytheonManufacturing Company, Newton, Mass, a corporation of DelawareApplication March 6, 1942, Serial No. 433,649

9 Claims. (01. 250-27.5)

This invention relates to a magnetron and more particularly to amagnetron in which the dimen-' sions of the internal structure determinethe frequency of the oscillations produced.

. In magnetrons of this kind it is often difficult to construct thecomponent parts thereof to dimensions which will produce a desiredfrequency within narrow limits, particularly when the scillationsproduced'are of extremely short 'wave lengths of the order ofcentimeters. Therefore it is desirable that some simple arrangement bedevised for tuning the magnetron after it has been completed to bringitsfrequency of oscilla- I tion to an exact predetermined value, eventhough as originally constructed said frequency may deviate somewhatfrom said predetermined value. It is also desirable that this tuning maybe accomplished while the magnetron .is actually in operation, without;the necessity of removing it from position between the usual magneticpole pieces.

An object of this invention is to devisea magnetron of the foregoingtype in which simple but effective tunin means are provided.

Another object is to devise a magnetron ofthis kind in which thefrequency of oscillation may be adjusted while the magnetron is inoperation and in position between the poles of its associated magnet. r

The foregoing and other objects of this invention will be bestunderstood from the following description of an exemplification thereof,reference being had to the accompanying drawing, wherein Fig 1 is avertical section through a mag-' I netron incorporating my invention,taken along line l-| of Fig. 2;

Fig. 2 is a cross-section taken approximately along line 2-2 of Fig. 1;and

Fig. 3 is a cross-section taken approximately along line 3-3 of Fig. 1.

The magnetron illustrated in the drawing comprises an envelope I whichis preferably made of a block of conducting material, such as copper.This block forms the anode of the magnetron. It likewise has hollow endsections which are covered by caps 2 and 3 likewise of conductingmaterial, such as copper. Between the hollow end sections of the block Iis located a central bridging portion 4 provided with a central bore 5within which is supported centrally thereof a cathode 6 which may be ofthe indirectly-heated oxide-coated thermionic type. The cathode issupported by a pair of lead-in conductors l and. 8. The conductor l issealed through a glass seal 9 .mounted at the outer end of icallyfastened within the wall of the block I ada pipe in hermetjacent theupper hollow end section. The lead-in conductor 8 is likewise sealedthrough a similar glass seal and pipe, not illustrated, adjacent-thelower' hollow end section. A plurality of slots ll extend radially fromthe central bore 5, and each of said slots terminates in a circularopen,- ing l2 extending through'the bridging portion ,4, In this way theanode structure is provided ,with a plurality of wedge-shaped arms 13,the faces of which cooperate as anode section with; the cathodefi. m

When such a magnetron is placed between suitable'magnetic poles l4 andI5 to create a longitudinal magnetic'field and the device is energized,oscillations are set up. These oscillations may .be led out from thetube by means of a coupling loop lfiextending into one of thecylindrical openings I2, and having one end thereof fastened to theinner wall of said opening. The other end of the coupling loop l6is-connected to the lead wire ll which passes through a glass seal I8mounted at the outer end of a pipe I 9 likewise hermetically fastenedthrough the Wall of the envelope l. An additional conducting pipe, notshown, may be electrically connected to the pipe l9 and form with thewire I! a concentric line through which the high frequency oscillationsgenerated by the magnetron may beflconducted to a suitable utilizationcircuit. I l h ,7

TA capacity exists between the cathode 6 and the face ofeach anodesection l3. -Also capacitances exist between the side Walls of each ofthe slots H. constitute inductances. The anode, therefore, is sodesigned and'spaced relative tothe cathode that the inductances andcapacitances described constitute circuits which are tuned. 'It isdesired that 'these'circuits shall be resonant at a definitepredetermined frequency at which the.

means may be provided whereby the normal fre- I quency of oscillation ofthe magnetron can be adjusted over fairly wide range even after themagnetron has been completed. For example, I have described and ;claimeda tuning arrange- The inner walls-of the openings [2 ment in mycopending application, Serial No. 425,071, filed December 31, 1941. Inaccordance with my present invention, this type of tuning is utilized inan arrangement which is very sturdy and which is capable of performingthe tuning even while the magnetron is in place between the pole piecesl4 and l 5.

In order to produce such tuning, a tuning member 20 is disposed with alower annular conducting face 2| held in juxtaposed position adjacentthe anode arms is at one side of the structure. The member 2i) isprovided with an upper threaded extension 22 which receives a centralthreaded portion of a plate 23. Surrounding the central threaded portionof the plate 23 is a depending cylindrical projection 24 which fitsrotatably into a corresponding central opening extending through the cap2. In order to maintain a hermetical seal and at the same time permitadjustment of the tuning member 20, a diaphragm 25 is provided. Thediaphragm 25 has a central opening which fits over the threaded portion22 so that said diaphragm may be hermetically sealed onto a shoulderformed on the tuning member 26 at the base of said extension 22. Theouter edge of the diaphragm 25 is likewise hermetically sealed onto ashoulder formed adjacent the outer edges of the cap 2. The diaphragm 25is preferably provided with a plurality of corrugations 26 so as to lendflexibility to said diaphragm, thus permitting a considerable motion ofthe central portion thereof which carries the tuning member 28, The cap2 is cut away at 27 to permit such movement of the diaphragm. The tuningmember 29 is likewise cut away at 28 to permit the upper end of thecathode 6 to extend therein. The member 29 is also provided with a slot29 which allows for the passage of the lead-in conductor 1. The outeredge of the plate 23 preferably extends slightly beyond the sides of theadjacent pole piece 14, and carries knurling which permits the plate 23to be readily turned in order to perform the desired tuning. Of courseit is understood that the magnetron is completed in the usual manner,and is completely evacuated. Therefore, a pressure will be exerted onthe plate 23 and the extension 22 of the member 2% which will tend topress said tunable structure inwardly against the body of the magnetron.This provides a biasing force which maintains the tunable structurefirmly in whatever position is determined by the degree of turning ofthe plate 23.

When the magnetron has been completed it is placed between the magneticpoles l4 and i and connected into a, suitable oscillating circuit,whereupon the system starts to generat oscillations. If it is found thatthe wave length generated by the magnetron deviates from the exact valuedesired as, for example, that fixed by the constants of the associatedcircuit, the magnetron may be tuned to that exact frequency merely byturning the plate 23. The threaded relationship between this plate andthe member 2% causes said member 26 to be raised or lowered, dependingupon the direction of the rotation of the plate 23. I have found thatsuch a structure produces an ample range of variation for all practicalpurposes in order to bring such a device in exact tuning with thefrequency which the device is intended to generate.

In accordance with my present understanding of the operation of thisinvention, varying the position of the conducting face 21 will vary thecapacitances of the anode structure as described above without affectingthe inductances thereof to the same degree. Therefore, varying saidcapacitances will tune the natural frequency of the magnetron in themanner desired.

Of course it is to be understood that this invention is not limited tothe particular details as described above as many equivalents willsuggest themselves to those skilled in the art. For example, theconductin surfaces moved adjacent elements of the anode structure mightbe disposed adjacent other portions of said anode structure. Likewiseelements which vary the inductance of the oscillating portions of theanode structure might be adjusted in accordance with the principles ofmy invention.

What is claimed is:

1. An electron discharge device comprising a sealed envelope containingan elongated cathode, adjacent anode elements, and a hollow resonatorinterconnecting said anode elements, a tuning element within saidenvelope adjacent said hollow resonator, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope, the median plane of said diaphragm being substantiallyperpendicular to the longitudinal axis of said cathode, and adjustablemeans connected to said diaphragm for flexing said diaphragm in adirection substantially perpendicular to said median plane for adjustingthe position of said tuning element.

2. An electron discharge device comprising a seal d envelope containinga cathode, adjacent anode elements having elongated electron-receivingfaces disposed about a common axis, and a hollow resonatorinterconnecting said anode elements, a tuning element within saidenvelope adjacent said hollow resonator, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope, said wall being transverse to said axis, the median plane ofsaid diaphragm being substantially parallel with the plane of that Wallof the envelope in which said diaphragm is sealed, and adjustable meansconnected to said diaphragm for flexing said diaphragm in a directionsubstantially perpendicular to said median plane for adjusting theposition of said tuning element.

3. An electron discharge device comprising a sealed envelope containinga cathode, adjacent anode elements having elongated electron-receivingfaces disposed about a common axis, and a hollow resonatorinterconnecting said anode elements, a tunin element within saidenvelope adjacent said hollow resonator, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope, said wall being transverse to said axis, the median plane ofsaid diaphragm being substantially parallel with the plane of that wallof the envelope in which said diaphragm is sealed, and adjustable meansconnected to said diaphragm external to said envelope for flexing saiddiaphragm in a direction substantially perpendicular to said medianplane for adjusting the position of said tuning element.

4. An electron discharge device comprising a sealed envelope containinga cathode, adjacent anode elements having elongated electron-receivingfaces disposed about a common axis, and a hollow resonatorinterconnecting said anode elements, a tuning element within saidenvelope adjacent said hollow resonator, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope,

dian plane of said diaphragm being substantially parallel with the planeof that Wall of the envelope in which said diaphragm is sealed, athreaded extension extending exteriorly of said 7 envelope and carriedby said diaphragm, and a cooperatively threaded member engaging saidextension and adapted upon rotation thereof to move said extension in adirection substantially perpendicular to said median plane for adjustingthe position of said tuning element.

5. An electron discharge device comprising a sealed envelope containinga cathode, adjacent anode elements having elongated electron-receivingfaces disposed about a common axis, and a hollow resonatorinterconnecting said anode elements, a tuning element within saidenvelope adjacent said hollow resonator, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope, said wall being transverse to said axis, the median plane ofsaid diaphragm being substantially parallel with the plane of that wallof the envelope in which said diaphragm is sealed, a threaded extensionextending exteriorly of said envelope and carried by said diaphragm, anda cooperatively threaded member, rotatably mounted on said envelope,engaging said extension and adapted upon rotation thereof to move saidextension in a direction substantially perpendicular to said medianplane for adjusting the position of said tuning element.

6. An electron discharge device comprising a sealed envelope containinga cathode, adjacent anode elements, and a hollow resonatorinterconnecting said anode elements, a tuning element within saidenvelope adjacent said hollow resonator, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope, the median plane of said diaphragm being substantiallyparallel with the plane of that Wall of the envelope in which saiddiaphragm is sealed, a threaded extensionextendin exteriorly of saidenvelope and carried by said diaphragm, and a centrally threaded plate,rotatably mounted on said envelope, engaging said threaded extension,and adapted upon rotation thereof to move said extension in a directionsubstantially perpendicular to said median plane for adjusting theposition of said tuning member, the plane of rotation of said platebeing substantially parallel with said median plane. a i

7. A magnetron comprising a sealed envelope containing a cathode,adjacent anode elements, and a hollow resonator interconnecting said 6anode elements, a tuning element within said envelope adjacent saidhollow resonator, said tuning element being mounted upon a flexiblediaphragm hermetically sealed in a wall of said envelope, the medianplane of said diaphragm being substantially parallel with the plane ofthat wall of the envelope in which said diaphragm is sealed, a threadedextension extending exteriorly of said envelope and carried by saiddiaphragm, a centrally threaded plate, rotatably mounted on saidenvelope, engaging said threaded extension, and adapted upon rotationthereof to move said extension in a direction substantiallyperpendicular to said median plane for adjusting the position of saidtuning member, and a magnet pole adjacent said plate for impressing amagnetic field on said magnetron, the edges of said plate extendingbeyond the sides of said pole to aiiord ready adjustment of said plate.

8. An electron discharge device comprising a sealed envelope containingan elongated cathode,

an adjacent multiplex anode structure, said anode structure comprising aconducting ring member from which a plurality of spaced anode armsproject inwardly toward a common central region in which the cathode issupported, the spaces betweensaid anode arms each defining a hollowresonator having an opening along one side communicating with saidcentral region, a tuning element within said envelope adjacent saidhollow resonators, said tuning element being mounted upon a flexiblediaphragm hermetically sealed in a wall of said envelope, and adjustablemeans connectedto said diaphragm for flexing said diaphragm foradjusting the position of said tuning element. 7

9. An electron discharge device comprising a sealed envelope containingan elongated cathode, an adjacent multiplex anode structure, said anodestructure comprising a conducting ring member from which a plurality ofspaced anode arms project inwardly toward a common central region inwhich the cathode is-supported, the spaces between said anode arms eachdefining a hollow resonator having an opening along one sidecommunicating with said central region, a tuning element within saidenvelope adjacent said hollow resonators, said tuning element beingmounted upon a flexible diaphragm hermetically sealed in a wall of saidenvelope, and adjustable means connected to said diaphragm external tosaid envelope for flexing said diaphragm for adjusting the position ofsaid tuning element.

PERCY L. SPENCER.

